Sensor systems for use in industrial field like automotive, in particular for use within engines must be capable to operate in a reliable and robust way for a reasonable life time in harsh media conditions.
A plurality of pressure sensor systems is available on the market. One type of pressure sensors that currently is available are front side exposed pressure sensors. Such pressure sensors typically provide a pressure sensing area and a signal processing area, relying on a multi-chip solution. One example of such a front side exposed pressure sensor is described in US2010/0300207. Problems related to such a sensor include the fact that such sensors have a relative large footprint, often require a plurality of different manufacturing techniques for fabricating them and that interconnections for signal transport between the pressure sensing area and signal processing area are sensitive and need to be protected. This typically is done using a gel. With this approach the gel has to be able to protect the bond pads. A second protection layer for the bond pads is to cover them with noble metals as for instance gold. However so far no automotive pressure sensor supplier seems to have found a good solution using gels or gold over pad metallization capable to handle the harsher media of future engines. A non exhaustive list of typical applications where the pressure sensor faces a harsher media is the so called TMAP sensor (Temperature Manifold Air Pressure, Turbo Manifold Air Pressure), the EGR pressure sensor (Exhaust Gas Recirculation) and the DPF pressure sensor (Diesel Particulate Filter).
In the prior-art front side exposed pressure sensors are disclosed, the presence of the necessary protection gels for the chip interconnects (bond pads), furthermore induces a temperature barrier avoiding local in-situ (at the place where the pressure is determined) measuring of the temperature, thereby leading to inaccurate data and requiring feeding in of external temperature measurements. Further the capability of these solutions to cope with harsh media depends on the gel used and today no protective solutions are available for the harsh conditions of future engines.
One alternative to the gel and over pad metallization is to make a back side exposed absolute TMAP pressure sensor like illustrated in the FIG. 18 of US2010/0300207 A1. In the solution described, a 2 chip concept is used and the ICs are directly bonded to the TMAP sensor housing, via's are connected on the cap to contact the piezo resistors and the cap is connected to the silicon by a fusion bonding process. However no exploration of improving the temperature aspect for this kind of sensors is found.
It furthermore is a disadvantage that the 2 chip concept is made directly on module level and requires significant space as well as calibration costs.
U.S. Pat. No. 8,146,439 provides a monolithic solution based on the so called APSM (Advanced Pourous Silicon Membrane) process and where the IC is bonded to a substrate using a chip on board approach. There is still a need for a compact solution, providing accurate protection of components and wherein accurate temperature calibration is possible.